The invention relates to a method for the determination of classification parameters or adaptation parameters for the classification of bank notes, in which properties of a bank note to be classified are ascertained and one class of several possible classes is determined by means of the classification parameters on the basis of the ascertained properties of the bank note. The invention further relates to an apparatus for carrying out the method, to a computer program for carrying out the method, as well as to a data carrier having the computer program.
Although the present invention is in principle employable without restriction for all types of sheet-like value documents, the present invention focuses particularly on bank notes, so that in the following instead of the general term “value documents” normally the term “bank notes” is employed for simplicity's sake, without this being understood as restrictive.
Classification methods are used in particular upon the detection and subsequent sorting of bank notes in bank note processing apparatuses. Here, at first physical quantities of the bank note to be classified are measured and a plurality of properties of the bank note is derived therefrom. Using the derived properties and with the aid of classification or adaptation parameters there is then ascertained a class, i.e. selected from several possible classes, and the bank note is assigned to this class. In a subsequent sorting process, the bank note can then be output in an output pocket provided for the corresponding class.
In such bank note processing apparatuses there is often taken a digital image of a bank note or of a region thereof by means of a suitable imaging sensor unit, for example a CCD or CMOS sensor. Such a digital bank note image consists of individual image points (pixels) with associated pixel values or intensity values, the pixels of colored images normally having assigned three pixel values. This bank note image is supplied in electronic form to a control and evaluation device of the bank note processing apparatus and can be employed by this, in addition to other measured properties of the bank note, for the classification of the bank note. For this purpose, on the basis of the digital image of the bank note or a part thereof and by means of the control and evaluation device of the bank note processing apparatus an optical or physical property of the bank note is quantitatively determined, for example an averaged intensity value in a certain region of the bank note image, and compared with an associated parameter, e.g. a threshold value, of a specified set of classification parameters.
Although digital bank note images are well suited for the determination of a plurality of properties of bank notes, e.g. the determination of the denomination of a bank note, certain properties can be determined in an only very restricted manner by means of a digital image of a bank note. For example for detecting adhesive strips on a bank note there is therefore normally employed a thickness sensor in the form of an ultrasonic sensor. The detecting and, where applicable, sorting out of bank notes provided with adhesive strips is desirable, since bank notes provided with adhesive strips can easily lead to jams in cash dispensing machines.
But before a bank note processing apparatus can be employed for processing bank notes, i.e. in particular for classifying, counting and sorting bank notes, a set of classification parameters must be created for the bank notes to be processed and be deposited for example in the control and evaluation device of the bank note processing apparatus. This procedure is known to the person skilled in the art also as an adaptation of a bank note processing apparatus. Ultimately, the trick with the adaptation is to chose the classification or adaptation parameters such that for as much bank notes as possible the class determined by the control and evaluation unit is equal to the “actual” class of a bank note. In other words: the classification or adaptation parameters determine the distribution of the bank notes over the classes defined by the classification parameters.